The invention relates to a method and an apparatus for the air treatment of filament yarn with yarn treatment nozzles having a continuous miniaturized yarn duct into which compressed air or gaseous fluid is introduced and a dominant twisting flow is produced in the yarn duct.
The production of yarn from synthetic fibres involves quite a number of basic stages. The individual continuous filaments are extruded via spinnerets from hot liquid thermoplastic polymer raw material and are then solidified in a cooling stage. A desired number of filaments are then combined to form a single thread or yarn which is either cut into staple fibre or left as a continuous filament. The staple product will not be described in detail hereinafter. It is subjected to processing steps similar to those whose basic principle is known from conventional natural yarn production. The very fine filament produced under high pressure as well as the yarn produced therefrom has a number of basic properties. These prevent direct use of the solidified unstretched filaments for the production of textiles. A chain molecular structure with low pre-orientation of the chain molecules is formed polymerization of a filament. If a yarn of this type is subjected to a more pronounced tensile stress, a considerable permanent change of length occurs. A typical representative of such a yarn which is designated POY (pre-oriented yarn) can be plastically stretched by a factor of 1:1.5 to 1.8.
30 years ago, it was normal to produce an LOY quality which even had to be stretched in a ratio of 1:3 to 3.8. The stretching process is a stage of operation which is essential for subsequent use for the production of textiles as the fabric (produced from unstretched yarn) would obviously be locally permanently elongated when first stressed. The second property is that the molecular orientation can be permanently changed at yarn temperatures of about 200xc2x0 C. and higher if the yarn is cooled immediately after an appropriate operation. The reduction in temperature below the glass transition point sets the changed molecular orientation produced under the influence of force so to speak. The third property is based on the second. The yarn is subjected to pronounced twisting in the hot state and a pronounced twist applied to the yarn. This operation has been employed worldwide for many decades and is known as the false twist method. Friction spindles are normally used as twisters nowadays. A spiral molecular orientation is created in the yarn owing to the twist which is forced mechanically on the yarn, so the individual filament can pass into a curved form after solidification and in the relaxed state, as shown schematically on the right of FIG. 1 according to the state of the art. The main result of the helical molecular orientation produced in this way is that the relaxed yarn can take on bulkiness and a crimped structure. The resultant product is described as false-twist-textured yarn and imparts a textile character to the end product.
A further particular property of synthetic fibre yarns is that the individual filament is sometimes very thin. To achieve high productivity in an economic manner, many filaments are produced continuously from a corresponding number of spinnerets and at very high rates. The spinning rate was 1000 m/min in the 60s. This has increased continuously ever since and is now between 3000 and 8000 m/min. Two particular branches of processing, among others, have arisen for textured yarn production. In one case, texturing is linked directly with the spinning process; in the other case (for titres  less than 1000, in particular  less than 334), texturing has to be separated from the spinning process. There is an excessively large discrepancy between spinning rate (POY yarn 3-4000 m/min) and the possible texturing rate in the second case. Supply bobbins therefore have to be produced after spinning. Final stretching and texturing is then carried out with the supply bobbins, separately from the filament spinning process in position and time. With coarse textured yarns, so-called BCF (bulked continuous filament) yarns, texturing can be carried out directly after filament extrusion, cooling and elongation. Typical BCF production rates are from 2500 to 5000 m/min. Simultaneous and sequential stretch texturing is known during false twist texturing. A characteristic feature of the two methods is that a heating zone and then a mechanical friction spindle for twist production are arranged in the direction of travel of the thread. During sequential stretch texturing (FIG. 1a) the yarn is stretched in a first stage and false twist texturing only carried out in a separate second stage (with respect to the yarn tension). As the twist acts in the direction of travel of the thread backwards to the next feed unit there before, a cooling zone can be arranged directly after the heating zone but in front of the twister. With simultaneous stretch texturing, stretching and texturing take place within the same stage, as shown in FIG. 1b. The highest possible yarn velocities can be achieved at present with the mechanical friction spindle. However, there is a natural limit to performance dictated mainly by the looping, the maximum permitted tensile stress on the yarn and the frictional resistance relative to the twist discs. If the performance of the twist discs which is to be transmitted exceeds a permitted level, surging occurs. A proportion of the already produced false twist with the travelling thread skips over the twist discs forwards in the direction of travel of the thread. This leads to an instantaneously reduced thread tension and simultaneously to a reduced twisting action. This effect is ultimately noticed as a defect on the finished textiles owing to periodically repeated differences, for example in colour.
The described methods are a combination of heating/cooling and a mechanically produced change in the molecular orientation. In contrast, air jet texturing is known, for example, from EP-PS 88 254. Air jet texturing utilizes the forces of air, in particular shock waves at the outlet from an air nozzle. The shock waves produce filament loops uninterruptedly on each individual filament. During air jet texturing, the yarn is guided into the air nozzle with a large overfeed. This overfeed is required during air jet texturing for the loops being formed in all directions, even toward the interior of the thread. The stability of the looped yarn is ensured by the loop action, but in particular by filament on filament friction. Production of the bulkiness in the false twist textured yarn, on the other hand, is based on the newly formed helical molecular orientation. The character of air jet textured yarn and of false twist textured yarn differs greatly. The two yarn qualities have their own particular fields of application. Apart from the qualitative differences (of air jet textured and false twist textured yarns), a main distinction between the two methods resides in the constructional dimensions of the texturing device. The mechanical friction spindle has dimensions which are a multiple of those of said air jet texturing nozzles. The mechanical friction spindle has extremely rapidly rotating parts in relation to the air jet texturing nozzle which does not require moving parts for its operation. The most obvious drawback of the mechanical friction spindle resides in the width dimension. If a parallel bundle of threads comprising many threads needs to be processed, the corresponding device is very wide. In addition to conventional long and deep stretch texturing machines, special machines are also constructed, for example for warp stretching, with which well over 1000 threads can be processed in parallel in a depth of 1 to 2 metres, but without texturing spindles. The same applies to warping devices. Warp stretching devices with a tangle arrangement show that air treatment can be carried out in a minimum of space. The desired aim is therefore to develop a compressed air element of suitably small shape, in particular with the possibility for optimized simultaneous processing.
U.S. Pat. No. 3,279,164 shows that attempts were made 40 years ago to utilize the capability of an air nozzle rather than the mechanical twister with an air nozzle to produce the known Helanca yarn. Attempts were made to work on the yarn with compressed air having at least half the speed of sound and at more than 200,000 rpm. The allegation that speeds of up to 1 million rpm have been attained is of interest. A large number of different constructional forms and air pressures from 1 to about 12 bar have been investigated from small cross section ducts to conventional nozzle passage cross sections. According to the technical teaching of the document, the sequential method was desired with a stretching procedure preceding the texturing zone. FIG. 48 which shows the critical operating conditions of the process is of particular interest. The overfeed was 15%. Pronounced variations in tension due to a twist doubling phenomenon occurred at a pressure exceeding 12 bar. Values between 8 and 12 bar were found to be the optimum pressure. The processing speed was usually 100 to 300 m/min. The speed of passage of the yarn which is extremely low by today""s standards was probably the main reason why this air false twisting method could not succeed in practice. An enormous increase in the performance of the mechanical twister did in fact occur at the same moment and led to a four-fold to five-fold increase in the processing speed, that is to over a thousand m/min within 30 years. The opinion has been upheld until now in the specialist sphere that the air treatment of filament yarns is not economically viable, in particular with respect to false twist texturing, as confirmed by the most recent specialist literature, for example Dr. Demir, Istanbul, (Chemical Fibers International, 46/996 Dr. Demir, pages 361-363).
The inventor has set himself the object of seeking ways and means of developing suitable methods of treating the yarn with air technology without mechanically moving parts and preferably also achieving a xe2x80x9cfalse twist texturexe2x80x9d. The aim was, in particular, simultaneous stretching and texturing, whether on the individual thread or on a bundle of threads. A part of the object was also to replace a mechanical twister with an air treatment nozzle for some applications.
The method according to the invention is characterized in that high pressure air higher than 14 bar is used and the filament yarn is stretch textured.
According to a particularly advantageous embodiment of the method, for the stretch texturing of filament yarn with at least one heating zone and a cooling zone and a twister the partially stretched yarn, for example POY yarn, is simultaneously stretched and textured or stretch textured as starting material, the twist being produced on the yarn by an air treatment nozzle having a feed pressure in the range of 14 to 80 bar. The nozzle according to the invention for the air treatment of filament yarns with a continuous air duct with tangential supply of compressed air into the yarn duct for producing a dominant twisting flow in the yarn duct, the yarn duct being miniaturized in design is characterized in that the nozzle is designed as a miniature nozzle for a high pressure range of more than 14 bar, in particular 20 to 50 bar.
A particularly preferred embodiment relates to a device, in particular a stretch texturing device, for the air treatment of filament yarns with at least one air treatment nozzle in miniaturized form, one air pressure device for a range of 20 to 50 bar and adjusting means for a selectable working pressure.
The inventor has also discovered that an upper meaningful limit for the air pressure actually existed with the former practice involving the air treatment of yarn by means of air treatment nozzles. In the first instance, a natural upper pressure limit of about 12 bar is noticed with pressure generators or compressors if compression is carried out in one stage. Secondly, all former known tests, including U.S. Pat. No. 3,279,164, showed that an increase beyond a pressure value over the range of 8 to 12 bar did not improve but rather impaired the result, depending on the concrete application. Therefore, it was not worth increasing the pressure over two or more stages, for example beyond 12 to 14 bar. To this was added the logic that, in each case, the increase in the air pressure cannot be used to increase the air speed despite the much higher production costs. The inventor accordingly adopted the reverse procedure. He recognized early that, in many applications, it was not the air speed alone or the increase in the air speed which must be decisive but rather a combination between this and the increase in the density of the air. The inventor was surprisingly able to discover, from large numbers of tests (contrary to the former notion) beginning from 100 bar with a steady reduction to the known values, noteworthy working windows which offered ideal conditions, in particular for the false twist texturing of yarns. The determined working windows are relatively narrow, in particular at low yarn velocities, and differ with respect to different yarn qualities. In the range of fine yarns, the window was frequently between 20 and 35 bar. This pressure can easily be produced with a two- or three-stage compressor. A further surprise resided in the fact that the good results were attained almost more easily at yarn velocities above 500 m/min and up to 800 m/min. This is therefore a velocity range which allows direct xe2x80x9cinline usexe2x80x9d, for example with known warp stretching devices. A further important point resided in the discovery that the air forces must be controllable to a much higher extent than in the state of the art. The inventor sought possible ways of achieving very high air twist intensities down to the lowest yarn ducts. A correspondingly high mass flow of air was produced with high speeds of rotation of the yarn in order to achieve this. It was noted that the twist is more intensive if the quantity of air is conveyed tangentially into the yarn duct via many small transverse ducts. However, to obtain a high mass throughput of air with small cross section transverse ducts, the pressures were tested to values within the specified range of 20 to 100 bar at the nozzle inlet. Tests have confirmed the correctness of the assumptions. High pressure which is produced in two or more stages, in particular above 20 bar, can be used economically with a miniaturized nozzle. In particular with a special geometry, as will be explained hereinafter. The improvement resides in the fact that the compressed air consumption can be markedly reduced with the same output.
The invention allows quite a number of advantageous designs and applications. It is particularly preferable if all transverse ducts merge tangentially into the yarn duct in such a way that a dominant, cyclonic twisting flow is produced and the filament yarn is actually false twist textured. The advantages can be implemented immediately, the air nozzle operating as an equal twister like a good mechanical twister. A working window in the range of 14 to 50 bar working pressure is particularly preferably determined once or repeatedly for establishing the range limits according to which the optimum working feed pressure can be accordingly established within the window. Out of the specified pressure conditions, the flow is always critical/over-critical in the narrowest cross section. The air speed is the same in the sonic/ultrasonic range. The air speed can be increased only to a limited extent with a given nozzle geometry at higher pressure. Furthermore, all experiments have confirmed the inventor""s assumption that the transferable force increases directly in proportion with the air density at least in a restricted range. The pressure range beneath the pressure window produces unsatisfactory texturing and, with a more pronounced reduction in pressure due to a steep increase in the thread tension, can very soon lead to the collapse of the texture. With low yarn velocities and high air feed pressure, the air forces are so great that the thread can be sheared off directly in the nozzle. The range over the pressure window results in surging, as already known with mechanical spindles. The best results could formerly be achieved if POY yarn was stretched textured simultaneously as starting material, with at least one heating zone, one cooling zone and subsequent air treatment nozzle in the direction of travel of the yarn, the yarn being false twist textured at a yarn feed rate of 400 to over 800 m/min via the air jet treatment nozzle. During the first attempts, without knowledge of the optimum working window, it was possible to achieve useful results only with the FOY quality under conditions similar to those described in U.S. Pat. No. 3,279,164. If the statements are correct, the tests confirm U.S. Pat. No. 3,279,164 which was disclosed to the inventor at a later stage. As the FOY yarn quality has rigid behaviour, i.e. can only be extended to a minimum, it was absolutely essential to use an overfeed so the shortening is compensated during twisting. The formation of a secondary twist is not unproblematic during this process.
According to the invention, an optimum working window is preferably determined first for each yarn quality. Optimum yarn tensions with respect to the yarn titre lie between 0.3 and 0.6 (cN/dtex) with a feed pressure between 20 and 40 bar. For this purpose, it is proposed that the yarn velocity, the working pressure and the yarn tension be selected as control variables with respect to yarn quality and appropriately optimized values be adjusted. The new invention also allows the false twist stretch texturing of yarn whether as an individual thread or as a bundle of threads. The yarn can be stretch textured in one stage in line, for example as a thread bundle immediately before being winded on a warp beam. The air treatment nozzle preferably has a higher number, for example 4 to 10 or more, preferably 4 to 8 transverse ducts. These are arranged either in a radial plane, in a plane parallel to the axis of the yarn duct or in a combination of the two. The transverse ducts open tangentially in the vicinity of the yarn duct wall so an intensive, maximum possible twisting flow is produced. A plurality of nozzles is advantageously arranged close together, i.e. nozzle to nozzle on a pressure distributing element for the parallel air treatment of a bundle of threads. Two or more nozzles can be combined in a nozzle block. It is also possible to form the nozzle element in one part and with a cylindrical surface shape, with sealing rings arranged in the two end regions of the surface shape, the compressed air supply being arranged between the two sealing rings. All previous tests yielded the best results when the yarn duct was designed symmetrically and in the form of a circular cylinder with a high surface quality in the central portion and when the apertures of the transverse bores were arranged in the central portion and the geometric position of all transverse bores was arranged identically with respect to tangential introduction into the yarn duct. The tangential ducts can lie in a common radial plane, in a slightly conical form or preferably in several mutually offset radial planes. According to a further embodiment, the nozzle element is designed in two parts and the tangential ducts arranged in a radial parting plane between the two parts. The yarn duct is preferably widened identically conically in the region of the yarn inlet and yarn outlet so the air treatment nozzle can be used for false twist texturing.
The invention also relates to a device for the air treatment of filament yarns and is characterized in that it comprises at least one or more air treatment nozzles in miniaturized form, an air pressure device for 14 to 80 bar, preferably 20 to 50 bar, and a controller, in particular for the yarn velocity, the yarn tensile force and a selectable working pressure with respect to the yarn quality to be processed. The device is preferably designed as a warp stretching device with a plurality of partially stretched, preferably POY yarns which are processed in parallel, or a corresponding bundle of threads, with at least one heater, one cooler and a nozzle block with a plurality of air treatment nozzles corresponding to the number of threads and a warp beam as well as a feed unit before the heater and after the nozzle block.